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Words to Know
asteroid
—A rocky body that orbits the Sun.An asteroid
is larger than a meteoroid but smaller than a planet.
asteroid belt
—A region of space between Mars and
Jupiter. Many asteroids are found there.
atmosphere
—The layer of gases that surrounds a planet
or other body in space.
comet
—A small ball of rock and ice that orbits the Sun.
core
—The innermost layer of Earth and some other
space objects.
crater
—A hole on the surface of a space body. It forms
when a smaller object crashes into a larger one.
crust
—The outermost layer of Earth.
day
—The time it takes a planet to complete one full
spin on its axis.
gas giant
—A large planet made primarily of hydrogen,
helium, and other gases. Jupiter, Saturn, Uranus, and
Neptune are gas giants.
gravity
—The force that pulls objects toward the center
of a planet or other body in space.
